Selective Catalytic Reduction
In Automotive
Zdeněk Král
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Selective Catalytic Reduction
…in general
• Wide technique of NOx removal
• Used everywhere, where NOx is produced (and undesired)
• Used mainly for exhaust gases (chimneys, exhausts, …)
• Selective
• We can select which molecule will be reduced (NOx, CO, CO2, SO2)
• Catalytic
• Reaction needs to be catalysed.
• Reduction
• NOx to N2
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SCR in automotive
• Reduction of NOx using reduction agent on a surface of solid catalyst in
presence of oxygen
• Summary equation: 4NO + 4NH3 + O2 → 4N2 + 6H2O
• Other SCR reactions:
8NH3+ 6NO2 → 7N2 + 12H2O
… plus many side reactions 2NH3 + NO + NO2 → 2N2 + 3H2O„fast SCR“
• Reduction agent
• Needed for high conversion rates
• NH3, HC (hydrocarbons)
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… a bit of History
• SCR was developer for industrial applications
• 70s - applied in thermal power plants in Japan
• Since 80s – widespread to Europe and USA
• First mobile aplications (not powerplants)
• 90s Korean cargo ships (diesel engine = electric
generator)
• Reason for this application - similar application as
in powerplants, steady state of engine operation
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How does SCR catalyst look like?
… of urea
• Ceramics carrier with active substance
• SiC, Cordierite
• „Mate“
• Heat resisting dense fibers
• Spacer for thermal dilatation
• Metal housing
• Stainless steel
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What is the active substance?
… of urea
• Several substances are catalytically active
enough to be used for SCR
• Cu and Fe zeolites (Cu-SSZ-13, Fe-ZSM5)
• Metal oxides (V2O5)
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• Mechanism is strongly dependent on exact composition of the
material
What is the mechanism?
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„State of the Art“
… of urea
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SCR in Automotive
Turbocharger
HOT END
Oxidation cat
DPF+SCR
SCR ASC
COLD END
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SCR in Automotive
ASC
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NH3-SCR in Automotive
Injection of AdBlue (32,5 % solution of urea in distilled water)
•Injection (200°C): H2N-CO-NH2 + H2O → 2NH3 + CO2
•1. hydrolysis: H2N-CO-NH2 + H2O → NH3 + HNCO
•2. acid w. water: HNCO + H2O → NH3 + CO2
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